Biology Reference
In-Depth Information
swollen form there is free exchange between the surrounding medium or
buffer and the interior of the viral capsid. Molecules smaller than 2 nm (that
is the diameter of the pores) can diffuse into the CCMV capsid. Structural
transition to the closed form leads to entrapment of the material within the
capsid; the molecules are
.
The dynamic properties of the CCMV capsid makes it an attractive
building block for applications ranging from materials to medicine. On the
materials side the capsids can be exploited to selectively and reversibly
entrap materials and allow spatially controlled synthesis of monodisperse
inorganic particles that may be difficult to obtain using common synthetic
procedures (see Chapters 5 and 6). With a viewpoint on medical applications,
the reversible gating may be exploited for the entrapment and controlled
release of therapeutic molecules. Not only the dynamic gating mechanism
of the particles is intriguing, using
gated
assembly methods, it has been
shown that the CCMV coat protein facilitates the construction of a range of
structures including tubes, rosettes, and sheets (Bancroft
in vitro
et al
., 1969).
..
Cowpea Mosaic Virus
: A Plant Virus
CPMV is a member of the Comovirus genus. Members are also known as plant
picorna-like viruses because they share similarities in structure, genome
organization, and replication strategy with animal picornaviruses (for
example
Poliovirus
, the infectious agent responsible for the human disease
poliomyelitis).
CPMV has a rather narrow natural host range; it infects legumes and was
first reported in black-eyed peas (
), which is also the plant used
for propagation of the particles. Geographically CPMV is found in Cuba, Japan,
Kenya, Nigeria, Surinam, Tanzania, and the USA, where the virus is transmitted
by leaf-feeding beetles, thrips, and grasshoppers (from DPV; http://www.
dpvweb.net and the ICTV; http://www.ncbi.nlm.nih.gov/ICTVdb).
The virions of CPMV are approximately 30 nm in size and are formed by
60 copies of two different types of coat proteins: S (one domain) and L (two
domains). The three domains of the two coat proteins form the asymmetric
unit and are arranged in a similar surface lattice to
V
.
unguiculata
= 3 viruses, except that
they have different polypeptide sequences; therefore, the particle structure
is described as
T
= 3 symmetry (Rossmann & Johnson, 1989). CPMV has a
bipartite positive-sense, single-stranded RNA genome (Lomonossoff &
Shanks, 1983; van Wezenbeek
P
., 1983).
CPMV wild-type and mutant particles are propagated in black-eyed
peas, in which the particles accumulate to high titers (1-2 g/kg infected leaf
material). In addition to the natural hosts, species from several families —
et al
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